Collector follower-type transistorized voltage regulator

ABSTRACT

A starting circuit is required in the voltage regulator of the so-called collector follower type, in which a voltage source is connected to an emitter input circuit of a regulating transistor and a load to its collector output circuit. In the voltage regulator of this invention, the starting circuit consists of a diode connected between the emitter input circuit and the collector output circuit of the regulating transistor. The diode supplies a starting current to the regulating transistor at a starting moment when an operating voltage is applied to the emitter input circuit of the regulating transistor, and it is reversely biased in the normal operating state of the regulating transistor, being electrically cut off. This invention attains effective voltage regulation even for a load current at a low level.

United States Patent Inventors KojiMatsumura Kodaira; Kunio Seki, l-ilgashimurayama, both of Japan AppLNo. 17,077

Filed Mar. 6, 1970 Patented Dec. 7, 1971' Assignee Hatachi, Ltd. Tokyo,Japan Priority Mar. 12, 1969 Japan 44/18324 COLLECTOR FOLLOWER-TYPE TRANSISTORIZED VOLTAGE REGULATOR 10 Claims, 8 Drawing Figs.

U.S. Cl 323/22 T, 317/3 l Int. Cl G05! 1/56, 605i 1/64 Field oi Search 320/40;

32l/l6, 18,45 S; 323/22 T, 22; 3l7/3l [56] References Cited UNITED STATES PATENTS 3,204, l 75 8/l965 Kuriger 323/22 T 3,344,340 9/1967 Webb 323/22 T Primary Examiner-Gerald Goldberg Anorney-Craig, Antonelli & Hill ABSTRACT: A starting circuit is required in the voltage regulator of the so-called collector follower type, in which a voltage source is connected to an emitter input circuit of a regulating transistor and a load to its collector output circuit. In the voltage regulator of this invention, the starting circuit consists of a diode connected between the emitter input circuit and the collector output circuit of the regulating transistor. The diode supplies a starting current to the regulating transistor at a starting moment when an operating voltage is applied to the emitter input circuit of the regulating transistor,

and it is reversely biased in the normal operating state of the regulating transistor, being electrically cut off. This invention attains effective voltage regulation even for a load current at a low level.

PATENTEUBEB 7l97l 3626278 sum 3 or 3 iNvE-N'roRS KOJ'I MATSHMARA Lnd Ku s s- ATTORNEYS COLLECTOR FOLLOWER-TYPE TRANSISTORIZED VOLTAGE REGULATOR This invention relates to a transistor voltage regulator which supplies a constant DC voltage to a load.

In a series voltage regulating circuit which supplies a constant voltage to a load regardless of any voltage variation in the voltage source by inserting a regulating transistor between the voltage source and load, one of the common circuits is the collector follower type, in which a load is connected to the collector side and a voltage source to the emitter side of a regulating transistor.

The voltage regulator of the collector follower type has a better ripple reduction factor than the usual emitter follower type, but a disadvantage in this circuit is that a starting circuit is required.

A circuit in which a resistor is inserted between the emitter and collector of a regulating transistor and the voltage supplying line are commonly used as a starting circuit. In either circuit, however, there is a defect in that the voltage regulating action is hindered at light load, i.e. the effective operation region is restricted by the load variation.

One object of this invention is to provide a series voltage regulator of the collector follower type where the voltage regulation is not affected-at light load.

Another object of this invention is to provide a series voltage regulator of the collector follower type possessing self protecting action against a short-circuiting of the load.

According to this invention, the starting current of the regulating transistor is provided by a diode which is inserted between the emitter input circuit and the collector output circuit of the regulating transistor, and in the normal operating state after the starting moment, the diode is reversely biased and substantially cut off. Thus, the undesirable loss of voltage regulation is prevented.

The above and other objects and features of this invention will be made more apparent from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a conventional voltage regulator.

FIG. 2 is a characteristic curve of the conventional voltage regulator shown in FIG. 1.

FIG. 3 is a circuit diagram of a voltage regulator according to the present invention.

FIG. 4 is a characteristic curve of the voltage regulator shown in FIG. 3.

FIGS. 5 to 8 are the circuit diagrams of the voltage regulators according to other embodiments of this invention.

In order to simply explain the unfavorable etfect which the starting circuit causes in connection with the voltage regulation at light load, a conventional voltage regulator as shown in FIG. 1 will be first explained with an emphasis on its operation.

In FIG. 1, Q, is a regulating transistor, Q, is an error signal amplifying transistor, R, and R, are error signal detecting resistors, R,, is an emitter resistor of the transistor Z is a reference diode, R, is a starting resistor inserted between the emitter and collector of the transistor 0,, 8 is a load, and the circuit 2 is a voltage source comprising an AC source 3, a rectifier 5, and a switch 4.

In this circuit, at the starting moment when the switch 4 is closed, a starting current (base current) is applied to the transistor 0, through the starting resistor R As the transistor 0, operates, the transistor Q, starts to operate. Namely, the operation of this voltage regulator is initiated by the starting resistor R,. Without this resistor R, neither the transistor Q, nor the transistor 0, starts to operate even if the switch 4 is closed, so that no prescribed voltage can be supplied to the load 8.

Therefore, the resistor R, is indispensable to the starting operation of the voltage regulator. However, this starting resistor has the disadvantage that it creates problems during voltage regulation at a light load, as seen in FIG. 2. When the load current is low (light load), the load terminal voltage V,,

rises, with the result that the voltage. regulating action is no longer available. Thus, in the voltageregulator of this type, the effective operating region of the load is reduced. So, the regulator becomes impractical at a light load.

Next, the voltage regulator according to the invention will be explained.

In FIG. 3, transistor Q, is a regulating transistor for controlling the voltage supplied'to the load, and a circuit] is a voltage detecting circuit formed in the collector circuit of the transistor 0,. The voltage detecting circuit comprises the resistors R, and R, for detecting the-collector voltage of the transistor 0,, a reference diode (Zener diode) Z for obtaining a reference potential, and a resistor R,,. The transistor 0, connected to the voltage detecting circuit I'amplifies the error signal detected by the voltage detecting circuit 1 up to the level of the base controlling signal of the transistor 0,. The emitter voltage of the'transistor Q, with respect to the collector voltage of the transistor Q, is made constant by the Zener diode Z. The base voltage of the transistor 0, follows the variation in the collector voltage of the transistor 0,. The circuit 2 is a voltage source circuit comprising an AC source 3 and a conventional rectifying circuit 5 for rectifying the AC signal from the source and supplying the rectified DC signal to the input terminals i,-i of the regulating circuit. The. circuit 7 is a potentiometer means comprising two resistors R,, and R,,. A,

The potential at the junction P, of this potentiometer 7 is set lower than that at junction P, between the detecting resistors R, and R, in the normal operating state after the switch 4 is turned on. D, is a diode for coupling the voltage detecting circuit I with the potentiometer'means 7. Since in the normal operating state the potential at P, is lower than that at P,, the diode D, is reversely biased. The circuit 8 is a load circuit connected to the output terminals 0,-0, the regulating circuit.

Let us consider the transient state (starting time) when the switch is turned on. In the initial state, the potential at P, is higher than that at P, since the transistor 0, is not operative. Thus, the diode D, is forwardly biased and supplies a base current to the transistor 0,, causing the transistor Q, to operate. A base current is given to the transistor Q, and the transistor Q, becomes conductive. Then, the voltage V, at the input terminal i, is transmitted as an output voltage V to the output terminal 0,. By the positive feedback action of the transistor 0,, theoutput voltage V, is reduced to a value predetennined by the resistors R, and R,, the reference potential V, of the Zener diode Z and the amplification factor of" the transistor Q2- In the normal operating state for the transistor.Q,, the output voltage V, is controlled to a prescribed voltage. At this moment, since the potential at P becomes higher than that at P,, the diode D, is reversely biased. Therefore, the diode D, is substantially cut off, giving neither electrical coupling therebetween nor troubles to the operation of the transistor 02' Thus, thepotentiometer means 7 and the diode D, constitute a starting circuit for giving a starting current to the transistors Q, and 0 when the switch 4 is turned on. In the normal operating state for the transistor 0,, the diode D, is substantially cut off so that the voltage regulating action is satisfactory even at a light load, as shown in FIG. 4.

By applying only a small starting current to the transistor 0, through the diode D,, the transistor Q, can operate normally by means of the positive feedback action of the transistor 0,, so that the values of resistors R, and R,, of the potentiometer can become large. Therefore, the power dissipation of the input circuit can be decreased.

FIGS. 5 and 6-show other embodiments of this invention. In FIG. 5, the terminal k of the diode D, is connected to the maximum potential level (output line of the detecting circuit 1.

FIG. 7 shows another preferred embodiment of this invention having a protecting circuit. The terminal k of the diode D, is connected to a point P having a lower potential than that of the output line 1,. Between the junction P and the output line a diode D is inserted, which is reversely biased in the normal operating state.

In this circuit let us consider that the output terminals 0, 0 are short-circuited. in this case, since the potential at the junction P becomes lower than that at P, of the potentiometer 7, the diode D is forwardly biased so as to supply a base current to the transistor Q However due to the presence of the diode D the current of the diode D is directed to the earth line I, through the diode D Therefore, the regulating transistor Q is protected from the breakdown, the base current thereof being cutoff.

Thus, this circuit has a self-protecting action against the short-circuiting of the output terminals. Since this self-protecting action is obtained by the diode D no complicated circuit is required.

FIG. 8 shows another embodiment of this invention, where the diode D is connected to the voltage detecting circuit 1 through the transistor Q At a starting moment the transistor Q, becomes conductive and passes a starting current to the transistor 0,. In the normal operating state the transistor 0;, is cut off. In this circuit when a short circuit occurs in the load circuit, the current flows only through the transistor Q}, but not through the transistors Q, and 0 However, the current through the transistor 0;, is largely suppressed by the resistor R so that the breakdown of the transistor O is prevented.

As described above, this invention can be applied to a case where the input source of the voltage regulator has a mechanical switch. The invention is characterized in that in the transient state when the mechanical switch is closed, the starting current is given to the regulating transistor by the diode means. This diode means may be the emitter-base junction or the collector-base junction of a transistor instead of an usual bipolar diode. For example, in the embodiment shown in FIG. 8, it is possible to use the emitter-base junction of the transistor 0;, as a diode means. Various other modifications of this invention may be made within the scope of this invention.

According to this invention, since it is possible to constitute a voltage regulator with relatively simple circuits, the application of this invention is particularly suited for the voltage regulator made by the integrated circuit technique.

What is claimed is:

l. A voltage regulator for use between a power source and a load comprising:

a regulating transistor having an emitter, a base and a collector for controlling the voltage to be supplied to the load, said power source being adapted to be connected to the emitter of said regulating transistor;

an output terminal connected to the collector of said transistor and adapted to connect the collector to said load;

voltage detecting means connected to the collector of said transistor for detecting a signal proportional to the potential difference between the potential at said output terminal and a predetermined reference potential;

amplifier means coupled between the base of said regulating transistor and said voltage detecting means for amplifying the resulting signal from said voltage detecting means and supplying the amplified signal to said base of said regulating transistor as a controlling signal, whereby the conductance of said regulating transistor is controlled by said controlling signal;

voltage source means providing a potential lower than a predetermined potential at the collector of the transistor in the normal operation state of said regulating transistor; and

first rectifying diode means coupled between said voltage detecting means and said voltage source means for supplying a starting current from said voltage source means to said regulating transistor through said amplifier means at the starting moment of said regulating transistor, the first diode means being reversely biased in the normal operation of said regulating transistor.

2. A voltage regulator. according to claim 1, wherein said voltage source means comprises a potentiometer connected between the emitter of said regulating transistor and a common reference potential.

3. A voltage regulator according to claim I, wherein said first diode means is connected between said voltage source means and a junction in the voltage detecting means, said junction having a lower potential than the collector potential in the normal operation state, and second rectifying diode means connected between said junction and said output terminal so as to be reversely biased in the normal operation of said regulating transistor.

4. A voltage regulator according to claim 3, wherein said voltage source means comprises a potentiometer inserted in the emitter input circuit of said regulating transistor.

5. A voltage regulator according to claim 2, wherein said first rectifying diode means is connected between said potentiometer and the collector of said regulating transistor.

6. A voltage regulator according to claim 2, wherein said voltage detecting means includes a second potentiometer connected between the collector of said regulating transistor and said common reference potential and said first rectifying diode means is connected between said potentiometer and said second potentiometer.

7. A voltage regulator according to claim 6, wherein said second potentiometer includes three resistors in series, said first rectifying diode means being connected to a point between first and second ones of said three resistors and said amplifier means being connected to a point between second and third ones of said three resistors.

8. A voltage regulator according to claim 7, further including second rectifying diode means connected between said point between first and second ones of said three resistors and said output terminal so as to be reversely biased in the normal operation of said regulating transistor.

9. A voltage regulator for use between a power source and a load comprising:

a regulating transistor having an emitter, a base and collector for controlling the voltage to be supplied to the load, said power source being adapted to be connected to the emitter of said regulating transistor;

an output terminal connected to the collector of said transistor and adapted to connect the collector to said load;

voltage detecting means connected to the collector of said transistor for detecting a signal proportional to the potential difference between the potential at said output terminal and a predetermined reference potential;

amplifying means having an input terminal coupled to said voltage detecting means and an output terminal connected to said base of the regulating transistor for amplifying the resulting signal from said voltage detecting means and supplying the amplified signal to said base of said regulating transistor as a controlling signal, whereby the conductance of said regulating transistor is controlled by said controlling signal;

voltage source means providing a potential lower than a predetermined potential at the collector of the transistor in the normal operation state of said regulating transistor; and

rectifying diode means connected between said voltage source means and said input terminal of the amplifying means for supplying a starting current from said voltage source means to said regulating transistor through said amplifying means at the starting moment of said regulating transistor, the rectifying diode means being reversely biased in the normal operation of said regulating transistor.

10. A voltage regulator according to claim 9, wherein said amplifying means comprises a second transistor having an emitter, a base and a collector, said base of said second transistor sewing as said input terminal of said amplifying means and said collector of said second transistor serving as said output terminal of said amplifying means. 

1. A voltage regulator for use between a power source and a load comprising: a regulating transistor having an emitter, a base and a collector for controlling the voltage to be supplied to the load, said power source being adapted to be connected to the emitter of said regulating transistor; an output terminal connected to the collector of said transistor and adapted to connect the collector to said load; voltage detecting means connected to the collector of said transistor for detecting a signal proportional to the potential difference between the potential at said output terminal and a predetermined reference potential; amplifier means coupled between the base of said regulating transistor and said voltage detecting means for amplifying the resulting signal from said voltage detecting means and supplying the amplified signal to said base of said regulating transistor as a controlling signal, whereby the conductance of said regulating transistor is controlled by said controlling signal; voltage source means providing a potential lower than a predetermined potential at the collector of the transistor in the normal operation state of said regulating transistor; and first rectifying diode means coupled between said voltage detecting means and said voltage source means for supplying a starting current from said voltage source means to said regulating transistor through said amplifier means at the starting moment of said regulating transistor, the first diode means being reversely biased in the normal operation of said regulating transistor.
 2. A voltage regulator according to claim 1, wherein said voltage source means comprises a potentiometer connected between the emitter of said regulating transistor and a common reference potential.
 3. A voltage regulator according to claim 1, wherein said first diode means is connected between said voltage source means and a junction in the voltage detecting means, said junction having a lower potential than the collector potential in the normal operation state, and second rectifying diode means connected between said junction and said output terminal so as to be reversely biased in the normal operation of said regulating transistor.
 4. A voltage regulator according to claim 3, wherein said voltage source means comprises a potentiometer inserted in the emitter input circuit of said regulating transistor.
 5. A voltage regulator according to claim 2, wherein said first rectifying diode means is connected between said poTentiometer and the collector of said regulating transistor.
 6. A voltage regulator according to claim 2, wherein said voltage detecting means includes a second potentiometer connected between the collector of said regulating transistor and said common reference potential and said first rectifying diode means is connected between said potentiometer and said second potentiometer.
 7. A voltage regulator according to claim 6, wherein said second potentiometer includes three resistors in series, said first rectifying diode means being connected to a point between first and second ones of said three resistors and said amplifier means being connected to a point between second and third ones of said three resistors.
 8. A voltage regulator according to claim 7, further including second rectifying diode means connected between said point between first and second ones of said three resistors and said output terminal so as to be reversely biased in the normal operation of said regulating transistor.
 9. A voltage regulator for use between a power source and a load comprising: a regulating transistor having an emitter, a base and collector for controlling the voltage to be supplied to the load, said power source being adapted to be connected to the emitter of said regulating transistor; an output terminal connected to the collector of said transistor and adapted to connect the collector to said load; voltage detecting means connected to the collector of said transistor for detecting a signal proportional to the potential difference between the potential at said output terminal and a predetermined reference potential; amplifying means having an input terminal coupled to said voltage detecting means and an output terminal connected to said base of the regulating transistor for amplifying the resulting signal from said voltage detecting means and supplying the amplified signal to said base of said regulating transistor as a controlling signal, whereby the conductance of said regulating transistor is controlled by said controlling signal; voltage source means providing a potential lower than a predetermined potential at the collector of the transistor in the normal operation state of said regulating transistor; and rectifying diode means connected between said voltage source means and said input terminal of the amplifying means for supplying a starting current from said voltage source means to said regulating transistor through said amplifying means at the starting moment of said regulating transistor, the rectifying diode means being reversely biased in the normal operation of said regulating transistor.
 10. A voltage regulator according to claim 9, wherein said amplifying means comprises a second transistor having an emitter, a base and a collector, said base of said second transistor serving as said input terminal of said amplifying means and said collector of said second transistor serving as said output terminal of said amplifying means. 